Plural gas stream dryer

ABSTRACT

A dryer for drying a food-substance foam mat which is transported on a perforate conveyor belt, with the mat pierced at the locations of perforations in the belt. The dryer includes: a drying chamber through which the mat and belt travel; a gas heater-blower system for developing a unitary flow of heated gas in the chamber, which flow is in a direction generally toward one side of the travel path for the belt and mat; and a corrugated perforate web which completely spans the drying chamber, and which functions to form, from the unitary gas flow mentioned, plural spaced-apart streams of gas that are directed toward the travel path.

[ Oct. 16, 1973 PLURAL GAS STREAM DRYER [75] Inventor: Thomas R. Miles, Portland, Oreg.

[73] Assignee: Foamat Foods, Corp., Corvallis,

Oreg.

[22] Filed: Dec. 3, 1971 [21] Appl. No.: 204,555

[52] US. Cl 34/218, 34/230, 34/233 [51] Int. Cl F26b 19/00 [58] Field of Search 34/156, 160, 201,

3,426,445 2/1969 Steffen 34/233 2,594,299 4/1956 Dungler... 34/160 3,266,559 8/1966 Osborne 34/216 3,069,786 12/1962 Nichols, Jr 34/236 Primary Examiner-Kenneth W. Sprague Assistant Examiner-James C. Yeung Attorney-Jon M. Dickinson [5 7] ABSTRACT A dryer for drying a food-substance foam mat which is transported on a perforate conveyor belt, with the mat pierced at the locations of perforations in the belt. The dryer includes: a drying chamber through which the mat and belt travel; a gas heater-blower system for developing a unitary flow of heated gas in the chamber, which flow is in a direction generally toward one side of the travel path for the belt and mat; and a corrugated perforate web which completely spans the drying chamber, and which functions to form, from the unitary gas flow mentioned, plural spaced-apart streams of gas that are directed toward the travel path.

4 Claims, 4 Drawing Figures PLURAL GAS STREAM DRYER BACKGROUND OF THE INVENTION This invention pertains to a dryer for drying a wet mat of a food-substance foam. More particularly, it pertains to means in such a dryer for forming a plurality of spaced-apartstreams of gas from a unitary gas flow, and for directing such streams against a mat of foam in the dryer.

One ofthe important commercial processes today for preparing various types of dehydrated food products includes the preparation ofa stable wet foam of a food substance, such as a blueberry foam, the laying out of such a foam in the form of a thin mat on a perforate conveyor belt, the perforation of the mat on the belt (at the locations of perforations in the belt), and the subsequent gas-circulation drying of the mat, with gas flowing over and about, and through the perforations-in, the

mat.

In the drying of such a foam mat, thereare a number of important factors to consider. In the interest of efficiency and economy, the drying process should take place in as short a time as possible. Drying must, of course, be thorough if a satisfactory end product is to result. As a practical matter, such efficiency, economy and thoroughness are best obtained in a forced-heatedgas-type drying system.

In any drying process employed, care must be taken to avoid damage to the relatively fragile structure of foam in such a mat. Thus, where circulated heatedgas is used, such gas must not impinge a mat with sufficient force to dislodge it from a conveyor belt, or to crumble or to otherwise break up the foam in the mat. It is desirable, however, where such a gas is used to develop a sufficiently high-speed gas flow through the perforations in .the foam (which perforations are aligned with perforations in a supporting belt as mentioned above), to prevent these perforations from closing while the foam in the mat is stillwet.

Still another factor to consider, along with the others just mentioned, is that the rate of moisture removal from the surface of a foam mat of the type described must not be so greatthatsurface-hardening or crusting occurs. Such hardeningcproduces a surface moisture barrier which then impairs proper drying of inner re- .gions in a mat.

SUMMARY OF THE INVENTION A general object of the present invention, therefore, is to provide novel'apparatus for drying a mat of foam such as the type of mat' generally described above, which apparatus takes the above-indicated factors into account in a practical and satisfactory manner.

According to a preferred embodiment of the invention, the proposed apparatus contemplates a dryer including a drying chamber through which a wet mat of foam which is to be dried is transported on a perforate traveling conveyor belt. Communicating with this drying chamber, and disposed toward one side of the path of travel defined for a mat by the conveyor belt, is apparatus for producing what might be thought of as a unitary, relatively low-velocity, flow of heated gas in the chamber, with such flow directed generallytoward the travel path mentioned. A unitary gas flow herein is considered to be that kind of flow which comprises, essentially, but a single unitary (i. e., nonfragmentary) stream of gas which may thought of as moving as a unit.

According to an important feature of the invention, interposed in the drying chamber, intermediate the conveyor belt and the means just mentioned for producing-a unitary flow of gas, is a special perforate web which completely spans the drying chamber, and which functions to form from the unitary gas flow mentioned a plurality of uniform, spaced-apart, higher velocity, streams of gas which are directed toward the belt. The particular web disclosed herein comprises a corrugated sheet containing, in plural substantially spaced-apart rows, a plurality of spaced-apart elongated slots, or openings. The rows of such openings extend transversely of the direction in which the conveyor belt travels, with adjacent openings in adjacent rows laterally overlapping one another. The plural gas streams formed by this web are distributed both longitudinally and transversely of the drying chamber.

Depending upon the particular drying application involved, the means for producing the unitary flow of gas, and the web for forming plural streams from the unitary flow, may together be disposed on either side of the conveyorbelt. In the particular dryer disclosed herein, thevarious parts are arranged whereby gas streams are directed toward the side of the belt which supports a mat of foam.

With the proposed apparatus, an efficient and effective drying operation results. The web in .the drying chamber produces multiple spaced-apart relatively high-velocity gas streams which are directed toward and substantially normal to one side of the belt. Such streams are distributed both longitudinally and transversely of the chamber. Gas flow adjacent the belt is thus characterized by plural spaced-apart regions of relatively high-velocity streams wherein flow is substantially normal to the belt, and intermediate these regions, zones of lower velocity gas flow, with flow in such zones being generally in a plane paralleling the travel path of the belt.

A mat of foam traveling through the chamber is consequently subjected to a sort of pulsed or buffeting gas flow; The high-speed streams in this flow promote rapid moisture removal, and generate even higher speed flow through perforations in a mat. The latter action tends to hold the perforations open in wet (and potentially flowable) foam. The lower velocity flow intermediate the streams produces a sort of surface-wiping action which promotes a somewhat slower moisture removal than that mentioned above. The overall result of this uniformly distributed pulsed gas flow is a thoroughly and properly dried, and intact, foam mat.

DESCRIPTION OF THE DRAWINGS These and other objects and advantages attained by the invention will become more fully apparent as the description which follows is read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a fragmentary side elevation illustrating a dryer employing the present invention, with a portion of an outside wall in the dryer broken away to illustrate details of construction; and

FIGS. 2, 3, and 4 are enlarged views, all on about the same scale, taken generally as indicated by lines 2-2,

I 33, and 4-4, respectively, in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION as contemplated herein, which is for drying a mat of a food-substance foam. Dryer comprises an elongated housing 12, wherein are formed a plurality of adjacent drying chambers which are distributed longitudinally of the housing. Three of such adjacent drying chambers in housing 12 are shown at l4, l6, 18. The tops of the three drying chambers shown are defined by substantially horizontal plates 20, and the opposite sides of these chambers are defined by spaced-apart substantially parallel upright plates 22. The opposite ends of a drying chamber are defined by spaced-apart substantially parallel upright plates 24 which occupy planes disposed substantially at right angles to the planes of plates 20, 22. Pairs of confronting plates 22 and 24 in a drying chamber are each spaced apart by a distance of about 4 feet. As a consequence, the transverse crosssectional area of each drying chamber is about 16 square feet.

ldicated generally at 26 in FIG. 1 is a portion ofa system in dryer 10 for supplying a flow of heated gas, such as heated air, to the tops of the drying chambers in the dryer. This system includes a plurality of conventional gas-heater-blower units, such as unit 28, which communicate with the tops of the drying chambers through ducts, such as duct 30. Suitable openings are, of course, provided in top plates 20. When operating, each gasheater-blower unit produces what might be thought of as a downwardly directed unitary flow of heated gas in its associated drying chamber, or chambers. Thus, a gas-heater-blower unit is also referred to herein as a directing means. Obviously, a single unit 28 may be used as desired to supply heated gas to one or more drying chambers. The unitary gas flow produced in chamber 16 by unit 28 is indicated generally by arrows 32 in FIG. I. As was mentioned earlier herein, the term unitary flow refers to flow of gas in a single unitary system. In the case ofdrying chamber 16, the unitary flow mentioned is that which occurs between and spans plates 22, 24 in the upper portion of the chamber. The speed of this flow in dryer 10 is about 125 feet-per-minute.

Referring now to FIGS. 1, 2 and 3 together, indicated generally at 34 is a portion ofa run ofa traveling perforate conveyor belt on which is supported a thin, flat mat 36 of a food-substance foam, such as a blueberry foam. The conveyor belt shown is a typical stainless steel belt which is suitably driven under power, at a linear travel speed of about 30 feet-per-minute, with the portion of its run which is shown in FIGS. 1, 2 and 3 traveling in the direction of arrow 38. The particular belt shown has a width of about 27V2-inches, a thickness of about 0.032-inches, and includes a central perforated region having a plurality of relatively uniformly spaced circular openings, or perforations, 340 with diameters of about 0.125-inches. The perforated region of the belt is about 40 percent open, has a width of about 26-inches, and is substantially centered relative to the opposite side edges of the belt.

In the particular dryer disclosed herein, belt 34 is what might be thought of as a catenary-type belt-- -supported only at its opposite ends. As can be seen in FIG. 2 for one side of the belt, the opposite side edges of the belt are disposed laterally inwardly from plates 22 which define the opposite sides of the drying chambers. Such construction eliminates the need for edge support structure for the belt, and minimizes problems attendant with gummy residue which may be left on the belt by foam. Such residue can introduce considerable friction in situations where edges of a belt ride on supports.

The foam in mat 36 comprises a stable, porous, wet foam which has been prepared in a'conventional manner through the mixing of nitrogen, and a suitable foaming agent with a liquid syrup or concentrate of blueberries. The particular mat illustrated has been extruded (in any suitable manner) onto the conveyor belt at a point upstream from the infeed end (not illustrated) of dryer 10, with a thickness of about of an inch. In accordance with the way in which the mat is formed on the belt, the mat illustrated herein has a width of about 25-inches, and is substantially centered laterally on the belt. As can be seen clearly in FIGS. 2 and 3, distributed throughout the foam mat are perforations, such as perforations 36a. These perforations in the mat are disposed at the locations of aligned perforations 34:: in the belt. Such perforations in the mat have been made at some point upstream from where the mat and belt enter the dryer in any suitable manner, as by piercing the mat with a gas stream directed from beneath belt 34. It will be apparent that these perforations expose a relatively large surface area for the escape of moisture from the mat.

Mounted within the various drying chambers in dryer 10 as contemplated herein are corrugated perforate webs 40. These webs are similar in construction, and considering the web shown in chamber 16, it comprises a corrugated sheet 42 which preferably is made of a metal such as aluminum or stainless steel. In the particular embodiment of the invention being described herein, sheet 42 contains 18 corrugations, and has a length and a width each of about 4 feet.

Formed in what might be thought of as the valleys of the corrugations herein, are rows of spaced-apart elongated openings, or perforations, such as those shown at 44. Each opening 44-has a length of about l%-inches, a width of about 3/16 of an inch, and is spaced from an adjacent opening in a row by a distance of about %-ll1CllS. With a sheet 42 containing 18 corrugations, it will be apparent that it contains 18 valleys, and hence 18 rows of openings 44. In the particular construction being described, nine of these rows each contain 25 openings, and the other nine rows each contain 26 openings. As illustrated in FIG. 2, rows containing 25 openings alternate with rows containing 26 openings, with each opening in a row offset from and longitudinally overlapping openings in adjacent rows. As can also be seen in FIG. 2, the rows of openings 44 extend laterally beyond the outer perforations 34a in belt 34. The center line spacing between adjacent rows is about 2.67-inches. Thus, each sheet 42 contains 459 slots. The collective cross-sectional area of these slots is about one square foot.

Webs are mounted in the drying chambers with the longitudinal axes of their corrugations extending transversely of the chambers. As can be seen in FIG. 1, the webs in adjacent chambers 14, 16, 18, are disposed at a substantially common elevation above belt 34. The webs are supportedin the chambers by means of pairs of angle members, such as angle members 46, 48, whose inturned flanges define elongated slots for freely receiving opposite side edges of the webs. As can be seen for the web disposed within drying chamber 16, a web substantially completely spans a drying chamber, both longitudinally and laterally. Opposite ends of the corrugated sheet in a web are disposed in overlapping relation with ends of the corrugated sheets of webs in adjacent drying chambers. Such overlapping is clearly illustrated in FIGS. 1 and 3.

Explaining now how the apparatus described herein performs, and referring particularly to FIGS. 1 and 3, mat 36 is transported by belt 34 in the direction of the arrow 38 through the various drying chambers in dryer 10. The drying action which takes place in these various chambers is similar, and considering what occurs in chamber 16, the unitary flow of air produced by unit 28 in chamber 16 above web 40 flows downwardly toward the web as indicated by arrows 32. It will be recalled that the velocity of this flow is about l25 feet-perminute. Web 40 functions to break up this unitary flow into a plurality of spaced-apart streams, each flowing through an opening 44 in the web. It will be apparent that these streams are distributed both longitudinally and transversely with respect to chamber 16. Because the collective cross-sectional area of openings 44 is less than the transverse cross-sectional area of chamber 16, a higher velocity characterizes flow in the streams passing through openings 44. More specifically, such flow has a velocity of about 2,000 feet-perminute.

As can be seen particularly in FIG. 3, where arrows indicate the character of gas flow about the web, the streams emanating from the bottom ends of openings 44 include portions that are directed substantially nor mal to mat 36, and portions which curve away and flow over and generally in the plane of the mat. The portions which flow substantially directly toward the mat produce a sort of pulsing action against the top of the mat as such travels through chamber 16. In addition, these portions produce even higher velocity gas flow through the aligned perforations in the mat and belt. This higher velocity flow through perforations 34a, 36a is also generally pulsed in nature, and functions not only to remove moisture from the mat, but also to maintain perforations 36a open. The portions of the streams coming from openings 44 which wipe along the surface of the mat are characterized by a somewhat lower flow velocity than the flow velocity in the openings.

The dryer construction described herein has been found through actual testing to produce a very effective and satisfactory drying of a mat of foam of the type described. Thorough drying of such a mat has been found to be obtainable in a relatively short period of time, and such drying has'been found'to be attainable without damage to the structure of the foam. The pulsed nature of the gas flow to which foam in a mat is subjected as such passes through a drying chamber maintains the perforations in the mat open to promote maximum moisture removal. Surface hardening does not occur.

The various dimensions and speeds set forth herein should be considered as illustrative only. It is important, however, that the web in a drying chamber substantially completely span the chamber, with the c'ollective cross-sectional area of its multiple perforations being less than the transverse cross-sectional area of the chamber. This relationship assures the proper formation of multiple gasstreams from a unitary gas flow. While a preferred embodiment of the invention has been described herein, it is appreciated that variations and modifications may be made without departing from its spirit.

I claim: I 1. In a dryer for drying a mat of foam, the dryer including a housing with a drying chamber therein, a perforate conveyor belt for transporting such a mat through said chamber, and means in the chamber for directing a unitary flow of gas toward one side of said belt:

means positioned intermediate said gas directing means and said belt, and disposed adjacent said one side of the belt, for intercepting said unitary flow and producing therefrom a plurality of spaced-apart streams of gas distributed longitudinally and transversely of the belt and directed toward said one side of the belt, said means consisting of a substantially planar web mounted within and spanning said chamber, said web having a plurality of longitudinally spaced, elongate openings therein, disposed in multiple, laterally spaced rows extending generally transverse to the belts longitudinal axis, with each opening in a row, viewed along a line paralleling said axis, at least partially overlapping an opening in an adjacent row. 2. The dryer of claim 1, wherein said web comprises a corrugated sheet mounted with its corrugations extending generally transverse to said axis, with said openings disposed in the valleys of the corrugations.

3. A dryer comprising a housing including a drying chamber, conveyor means defining a path for the transport of foam material to be dryed through said chamber, said means comprising a perforate conveyor belt, means for producing a unitary flow of gas in said chamber and directing said flow toward one side of said belt, plural-gas-stream-forming means mounted within and spanning said chamber, and disposed adjacent said one side of the belt, said plural-gas-streamforming means consisting of a substantially planar web positioned intermediate said directing means and said one side of the belt, and having a plurality of longitudinally spaced, elongate openings distributed thereover, disposed in multiple, laterally spaced rows extending generally transverse to the belts longitudinal axis with each opening in a row, viewed along a line paralleling said axis, at least partially overlapping an opening in an adjacent row. 4. The dryer of claim 3, wherein said web comprises a corrugated sheet mounted with its corrugations extending generally transverse to said axis, with said openings disposed in the valleys of the corrugations. 

1. In a dryer for drying a mat of foam, the dryer including a housing with a drying chamber therein, a perforate conveyor belt for transporting such a mat through said chamber, and means in the chamber for directing a unitary flow of gas toward one side of said belt: means positioned intermediate said gas directing means and said belt, and disposed adjacent said one side of the belt, for intercepting said unitary flow and producing therefrom a plurality of spaced-apart streams of gas distributed longitudinally and transversely of the belt and directed toward said one side of the belt, said means consisting of a substantially planar web mounted within and spanning said chamber, said web having a plurality of longitudinally spaced, elongate openings therein, disposed in multiple, laterally spaced rows extending generally transverse to the belt''s longitudinal axis, with each opening in a row, viewed along a line paralleling said axis, at least partially overlapping an opening in an adjacent row.
 2. The dryer of claim 1, wherein said web comprises a corrugated sheet mounted with its corrugations extending generally transverse to said axis, with said openings disposed in the valleys of the corrugations.
 3. A dryer comprising a Housing including a drying chamber, conveyor means defining a path for the transport of foam material to be dryed through said chamber, said means comprising a perforate conveyor belt, means for producing a unitary flow of gas in said chamber and directing said flow toward one side of said belt, plural-gas-stream-forming means mounted within and spanning said chamber, and disposed adjacent said one side of the belt, said plural-gas-stream-forming means consisting of a substantially planar web positioned intermediate said directing means and said one side of the belt, and having a plurality of longitudinally spaced, elongate openings distributed thereover, disposed in multiple, laterally spaced rows extending generally transverse to the belt''s longitudinal axis with each opening in a row, viewed along a line paralleling said axis, at least partially overlapping an opening in an adjacent row.
 4. The dryer of claim 3, wherein said web comprises a corrugated sheet mounted with its corrugations extending generally transverse to said axis, with said openings disposed in the valleys of the corrugations. 